phrynosoma cornutum

Horned lizard

Horned lizards (Phrynosoma) are a genus of the Phrynosomatidae family of lizards. The horned lizard is popularly called a "horned toad," "horny toad", or "horned frog," but it is neither a toad nor a frog. The popular names come from the lizard's rounded body and blunt snout, which make it resemble a toad or frog. (Phrynosoma literally means "toad-bodied.") The spines on its back and sides are made from modified scales, whereas the horns on the heads are true horns (i.e. they have a horny core). There are 14 species of horned lizards in North America, 8 of which are native to the United States. The largest-bodied and most widely distributed of the U.S. species is the Texas horned lizard (P. cornutum).

Description

Horned lizards are morphologically similar to the Australianthorny devil (Moloch horridus), but are only distantly related. They also have other unique similarities, such as being sit-and-wait predators and preying upon ants, and so the two species are considered a great example of convergent evolution.

Protection against predation

Horned lizards use a wide variety of means to avoid predation. Their coloration generally serves as camouflage. When threatened, their first defense is to remain still and hope to avoid detection. If approached too closely, they generally run in short bursts and stop abruptly to confuse the predator's visual acuity. If this fails, they puff up their body to cause it to look more horny, making it appear larger and more difficult to swallow. At least four species are also able to squirt an aimed stream of blood from the corners of the eyes for a distance of up to 3 feet. They do this by restricting the blood flow leaving the head, thereby increasing blood pressure and rupturing tiny vessels around the eyelids. This not only confuses predators, but also the blood tastes foul to canine and feline predators. It appears to have no effect against predatory birds. To avoid being picked up by the head or neck, horned lizards duck or elevate their head and orient their cranial horns straight up, or back. If a predator tries to take it by the body, the lizard drives that side of its body down into the ground so that the predator cannot easily get its lower jaw underneath the lizard.

In California, Texas, and other states, horned lizards are considered threatened and given state protection, though none are on the federal endangered species list. The Texas horned lizard has declined in about 30% of its range, though there is some indication it may be making a comeback. Some California species are also in decline. The decline is usually blamed on development/destruction of habitat, the spread of non-native South American ants which compete and war with the harvester ant, and the overuse of pesticides which kill harvester ants. In California, the introduced species is the Argentine ant. In Texas, it is the Argentine ant and the Brazilianfire ant. Both species are highly aggressive and fiercely territorial, and prey on harvester ant queens, destroying the horned lizard's principal source of food!!